Cored direct positive emulsion for photosolubilization process

ABSTRACT

This invention relates to a photosolubilization process for the production of images by means of exposing emulsions having a lowered rate of solution because of a silver salt which is less soluble than silver chloride, after which exposed elements are removed with a silver halide solvent to produce an image. The sensitivity of this emulsion is increased by internal sensitivity specks in the composite grain structure of the silver halide which specks are the core of the grains chemically ripened as by gold and sulfur sensitization. The processing of the exposed photographic material being carried out under otherwise usual conditions.

United States Patent [72] inventor Erik Moisar Cologne-Flittard, Germany [21] Appl. No. 760,216

[22] Filed Sept. 17, 1968 [45] Patented Oct. 26, 1971 [7 3] Assignee AGFA-Gevaert Aktlengesellschait Leverkusen, Germany [32] Priority Oct. 4, 1967 [33] Germany [54] CORED DIRECT POSITIVE EMULSION FOR PHOTOSOLUBILIZATION PROCESS 3,206,313 9/1965 Porter, et al. 96/107 3,367,778 2/1968 Berriman 96/64 FOREIGN PATENTS 1,027,146 4/1966 Great Britain 1,031,901 6/1966 Great Britain Primary Examiner-Norman G. Torchin Assistant Examiner-Won H. Louie, Jr. Attorney-Connolly and Hutz ABSTRACT: This invention relates to a photosolubilization 4 Claims, 1 Drawing Fig. process for the production of images by means of exposing [52] US. Cl 96/64, emulsions having a lowered rate of Solution because f a silver 96/10'7, 96/108 salt which is less soluble than silver chloride, after which ex- [51] Int. Cl 603C 5/24 posed elements are removed i a silver halide solvent to [501 Field of Search 96/64 produce an image. The sensitivity of this emulsion is increased 108 by internal sensitivity specks in the composite grain structure of the silver halide which specks are the core of the grains [56] Rderences Cited chemically ripened as by gold and sulfur sensitization. The UNITED STATES PATENTS processing of the exposed photographic material being carried 3.155507 11/1964 Blake 9 6/67 out under otherwise usual conditions.

0 1 a I l a I 2 3 4 5 5 PATENTEnnm'zslsn' 3.615.518

0 J J I 2 3 4 5 6 INVENTOR.

ERIK MO/SAR.

CORED DIRECT POSITIVE EMULSION FOR PHOTOSOLUBILIZATION PROCESS This invention relates to a silver halide emulsion with improved sensitivity for the solubilization process.

The photosolubilization process for producing photographic images comprises exposing imagewise elements carrying emulsions containing silver halide crystals previously caused to have a lowered rate of solution in a silver halide solvent by treatment with an organic compound capable of forming a silver salt which is less soluble in water than silver chloride, and then treating the exposed elements with a silver halide solvent to remove silver halide selectively from the exposed areas. These processes are capable of yielding positive photographic images of silver halide since on exposure to actinic radiation the rate of solution of the silver halide is increased in the exposed areas. This positive silver halide image can subsequently be intensified by various means, e.g., by reducing the silver halide to metallic silver. The elements are sensitive only to the shorter end of the visible spectrum, i.e., they cannot be exposed by red, orange, or yellow light, and have very little sensitivity to green light.

The photosolubilization process and suitable organic compounds are described in detail in British Pats. Nos. 1,031,902; 1,031,902; 1,031,903; 1,078,231 and 1,117,320.

The photosolublization process described above for the preparation of direct positive images is, however, of limited utility because the sensitivity of suitable photographic emulsions is not sufficient.

It is among the objects of the present invention to improve the sensitivity of silver halide emulsion to be used for the photosolubilization process.

We now have found that silver halide emulsions, the grains of which contain ripening nuclei or sensitivity specks only in their interior are particularly suitable for use in the photosolubilization process.

Photographic emulsions cotaining ripening nuclei or sensitivity specks only inside the silver halide grains are known per se. They can be prepared, for example, by mixing a coarsegrained silver halide emulsion which has been chemically ripened and which contains superficial sensitivity specks, with a finegrained emulsion, followed by physical ripening of the mixture. The coarser grains then grow at the expense of the smaller ones and the unripened fine-grained emulsion is deposited on the ripened coarse-grained emulsion. Processes of this type have been described, for example, in British Pat. No. 1,011,062.

Photographic silver halide emulsions, the silver halide grains of which have a so-called composite grain structure, are particularly suitable for use in the present invention. Processes for the preparation of such emulsions are described in British Pat. No. 1,027,146. In such a process, a fine-grained emulsion with a narrow range of grain sizes is first prepared; after interruption of precipitation, chemical ripening is carried out and precipitation is then continued. An emulsion containing silver halide grains which contain a chemically ripened core covered by an unripened layer of silver halide is obtained.

Preferred are emulsions, the grains of which contain a core which is chemically ripened with gold and/or sulfur sensitizers. The gold and sulfur sensitization is described for example by C.E.K. Mees, The Theory of the Photographic Process," New York, The MacMillan Company, revised edition, 1954, pages 112 seq.

Particularly suitable are the composite grain emulsions described in examples 3 and 4 of British Pat. No. 1,027,146 or the emulsions of examples 1 and 2 ofU.S. Pat. No. 3,206,313.

Precipitation of the silver halide is advantageously carried out by the process described by Klein and Moisar in Berichte der Bunsengesellschaft fuer physikalische Chemie, Vol. 67,(l963), pages 349 seq.

The photosolubilization process comprises the steps of:

a. Exposing, imagewise, to actinic radiation, a photographic element containing silver halide crystals previously made relatively less soluble in a silver halide solvent by treatment with an organic compound capable of forming silver salt and whose silver salt is of lower solubility in water than silver chloride, and

b. Treating said element with an aqueous solution of a silver halide solvent, effecting solubilization of the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive image comprised of silver halide is produced; said organic compound being characterized in that when admixed with an aqueous silver halide dispersion it protects the silver halide grains to such an extent that when a silver halide dispersion protected by said compound is treated with 10 percent (by weight) aqueous sodium thiosulfate, at least three times the amount of silver halide remains undissolved as in a similar dispersion successively treated with 5 percent sodium hypochlorite and 10 percent aqueous sodium thiosulfate, after vigorous agitation of the dispersion for 30 seconds at 25 C. The dispersion so successively treated clears whereas the other dispersion remains turbid. The selected organic compound may be further characterized as being a compound whose silver salt is less soluble in water than silver chloride crystals. The treated residual silver halide image may then be converted to metallic silver, dyed or toned images. The solvent for the silver halide layer is an aqueous solution of a silver halide solvent, e.g., sodium thiosulfate.

The photosolubilization process is, in all probability, based on a reaction of halogen, particularly bromine, formed upon exposure with the organic silver compound being less soluble than silver halide. The decomposition of that silver compound results into a higher solubility of the light-sensitive silver halide at the exposed areas as compared with the unchanged silver halide in the unexposed parts of the layer.

Thus, the sensitivity of an emulsion for the photosolubilization process highly depends on its capability to form upon exposure halogen as fast as possible. Furthermore, the halogen must not be used up by other possible reactions. Reactants for such undesired reaction are for example silver nuclei capable of reacting with halogen to form silver halide. Silver halide emulsion, for example, which are prefogged and which contain a surface latent image generally show a decreased speed if used for the photosolubilization process. it was all the more unexpected that silver halide emulsions, the silver halide grains of which contain an internal latent image or internal sensitivity specks have an highly increased sensitivity in the photosolubilization process.

The photographic materials to be used in the process according to the invention are prepared in the usual manner. Further processing after the photosolubilization step is also performed in the usual manner.

Details of the materials and the process are described in the above-mentioned British patent specifications.

Example 600 ml. of 3N Agn03 solution and 600 ml. of 3N KBr solution are introduced at a rate of 330 ml. per hour at a constant EMF of +160 mv. (silver electrode/saturated calomel electrode) into 500 ml. of a 4 percent gelatin solution at 600 C., using metering pumps. When ml. of AgN03 and KBr solution have been added, precipitation is interrupted. One ml. of 10 2 mol of Na3 Au(S203 )2 solution is added to the emulsion and the emulsion is kept at 50 C. for 30 minutes. Precipitation is then continued as described above.

The emulsion is solidified and washed with water in the usual manner. 0.1 kg. of the washed emulsion is treated with 1.1 liter of 5 percent gelatin solution and with 10 ml. of a 1 percent solution of phenyl mercaptotetrazole in 30 ml. of alcohol and cast to form a film in the usual manner. An unexposed sample is not fixed to any noticeable extent when treated with 5 percent sodium thiosulfate solution for 2 minutes whereas solution of the silver halide occurs in the exposed areas.

Sensitometric tests yield the density curve 1 shown in the attached figure. Curve 2 of the figure is obtained with an emulsion which has been prepared in the same manner but without chemical ripening of the silver halidexworlting up was again carried out in the same manner. ln the figure, the axis of ordinates represents the density and the axis of abscissas the intensity of exposure of log 11. The figure shows clearly the surprising increase in sensitivity obtained.

I claim:

1. In the photosolubilization process by exposing imagewise to actinic light a supported photographic silver halide solidified emulsion layer containing silver halide grains of a composite grain structure made relatively less soluble in sodium thiosulfate by treatment with an organic compound capable of forming a silver salt of lower solubility in water than silver chloride and treating said exposed layer with an aqueous solution of a silver halide solvent, thereby dissolving the silver halide in the more exposed areas at a rate substantially greater than in the less exposed areas until a positive silver halide emulsion is produced, the improvement consisting of chemically sensitizing the silver halide emulsion layer containing the silver halide grains prior to solidification by mixing with a sensitizer which chemically ripens the silver halide grain cores while the shell of the silver halide grain is unripened, to provide silver halide grains with ripening nuclei solely in the grain interior.

2. The process of claim 1, wherein the organic compound for treatment of the silver halide grains is phenyl mercaptotetrazole.

3. The process of claim 1, wherein the silver halide core was ripened with gold and/or sulfur compounds.

4. The process of claim 3, wherein the core of the silver halide grain was ripened with a gold thiosulfate complex compound.

i l i t I 

2. The process of claim 1, wherein the organic compound for treatment of the silver halide grains is phenyl mercaptotetrazole.
 3. The process of claim 1, wherein the silver halide core was ripened with gold and/or sulfur compounds.
 4. The process of claim 3, wherein the core of the silver halide grain was ripened with a gold thiosulfate complex compound. 